This invention relates generally to devices for the infusion of drugs into the human body, and, more particularly, to pump driven devices for the highly accurate infusion of small quantities of drugs.
The administration of drugs to a patient can be accomplished through a variety of methods, including gravity, mechanical pumps, pressurized gases and osmosis. A gravity dispenser utilizes the force of gravity to dispense a drug suspended above the patient. The delivery rate of the drug is adjusted by means of the pressure head, the height of the drug above the patient, and by a restriction of the outlet line leading to the patient. However, the delivery rate of the gravity dispenser is difficult to control accurately because of changes in the height of the drug as it is dispensed to the patient, changes in the posture of the patient and even variations in the back pressure of the patient's blood. More importantly, however, the patient is greatly restricted in mobility, since the drug must be constantly suspended in a container above the patient. A typical controller for adjusting the delivery rate of the gravity force dispenser is disclosed in U.S. Pat. No. 4,300,552 to Cannon.
Other methods for administering drugs eliminate the need for suspending the drug above the patient and, therefore, greatly improve the mobility of the patient. Mechanical pump dispensers generally consist of an electrically driven mechanical pump. These pumps provide accurate control of the delivery rate of the drug, but incorporate moving parts, which can wear out and break down. These pumps also consume relatively large amounts of power. Other dispensers employ a pressurized gas to administer the drug to the patient. Generally, these dispensers are large and bulky, and not easily portable. Furthermore, regulation of the delivery rate is often difficult. Typical pressurized gas dispensers are disclosed in U.S. Pat. No. 2,766,907 to Wallace, Jr. and U.S. Pat. No. 4,237,881 to Beigler et al.
Osmosis driven dispensers depend on solutes that exhibit an osmotic pressure gradient against water. The delivery rate provided by these dispensers is determined by the type of solute used and, therefore, the delivery rate cannot be varied during operation. Representative osmotic dispensers are disclosed in U.S. Pat. No. 3,995,632 to Nakano et al., U.S. Pat. No. 4,034,756 to Higuchi et al. and U.S. Pat. No. 4,439,196 to Higuchi. Electrically controlled osmotic dispensers are disclosed in U.S. Pat. No. 3,923,426 to Theeuwes and U.S. Pat. No. 3,894,538 to Richter.
Many patients require a continuous infusion of small quantities of drugs over a period which may be many hours or even several days in duration. Such drugs sometimes must be dispensed at constant, precisely-controlled rates; in other cases, the drugs must be dispensed in a cyclical, pulsating fashion, or at a controlled variable rate. Accordingly, there is a need for a portable, implantable drug dispenser that can accurately dispense small quantities of drugs at a desired rate extending over a relatively long period of time.